When I saw your post I thought "Yes, that's true. But it would be more efficient to declare the @good_nums array outside the look and just empty it". Luckily I did not go ahead and post that, but run a benchmark (In Perl 5.8, ActivePerl build 804, Win2kServer): 

use Benchmark;
use strict;

sub arrayInit {
    foreach (1..1000) {
        my @list;
        foreach (1..10) {
            push @list, $_;
        }
    }
}

sub arrayUndef {
    my @list;
    foreach (1..1000) {
        foreach (1..10) {
            push @list, $_;
        }
        undef @list;
    }
}

sub arrayEmpty {
    my @list;
    foreach (1..1000) {
        foreach (1..10) {
            push @list, $_;
        }
        @list = ();
    }
}

sub scalarInit {
    foreach (1..1000) {
        my $sum;
        foreach (1..10) {
            $sum += $_;
        }
    }
}

sub scalarUndef {
    my $sum;
    foreach (1..1000) {
        foreach (1..10) {
            $sum += $_;
        }
        undef $sum;
    }
}

sub scalarEmpty {
    my $sum;
    foreach (1..1000) {
        foreach (1..10) {
            $sum += $_;
        }
        $sum = 0;
    }
}

timethese 1000, {
    arrayInit => \&arrayInit,
    arrayUndef => \&arrayUndef,
    arrayEmpty => \&arrayEmpty,
    scalarInit => \&scalarInit,
    scalarUndef => \&scalarUndef,
    scalarEmpty => \&scalarEmpty,
}
__END__

Benchmark: timing 1000 iterations of arrayEmpty, arrayInit, arrayUndef
+, scalarEmpty, scalarInit, sca
larUndef...
arrayEmpty: 15 wallclock secs (13.97 usr +  0.00 sys = 13.97 CPU) @ 71
+.58/s (n=1000)
 arrayInit: 13 wallclock secs (13.45 usr +  0.00 sys = 13.45 CPU) @ 74
+.35/s (n=1000)
arrayUndef: 16 wallclock secs (15.70 usr +  0.00 sys = 15.70 CPU) @ 63
+.68/s (n=1000)
scalarEmpty:  9 wallclock secs ( 9.30 usr +  0.02 sys =  9.32 CPU) @ 1
+07.26/s (n=1000)
scalarInit: 10 wallclock secs ( 9.36 usr +  0.01 sys =  9.37 CPU) @ 10
+6.68/s (n=1000)
scalarUndef: 10 wallclock secs ( 9.43 usr +  0.00 sys =  9.43 CPU) @ 1
+06.01/s (n=1000)

[download]
So once again I was wrong :-|

Thanks for making me try.

Jenda
Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.
   -- Rick Osborne

Edit by castaway: Closed small tag in signature

In reply to Re: Re: value accumulation by Jenda
in thread value accumulation by Anonymous Monk

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